The purpose of this project is to understand the mechanisms which determine the disposition of environmental chemicals in various animal species and to develop pharmacokinetic models for these chemicals. 1) After developing pharmacokinetic models in several species, it may be possible to extrapolate disposition of chemicals to other species, and, ultimately, to man. The prediction of the accumulation in man after low-level chronic exposure could then be done. Pharmacokinetic information (models) can be very useful in the design and interpretation of toxicity studies. The topics of present interest are: a) disposition of several polychlorinated biphenyls in the rat, mouse, dog, and monkey. b) development of pharmacokinetic models for the polychlorinated biphenyls in these species.